Electrolytic process of detinning.



H. GOLDSCHMIDT.

ELECTROLYTIC PROCESS 0F DETINNING.

APPucATlo FILED ris. 5. |908.

1,160,400, Patented Nov. 16, 1915.

2 SHEETS-SHEET l.

H. GOLDSCHIVHDT. ELEcTRoLYTlc PROCESS 0F DEHNNING.

APPLICATION FILED FEB. 5. 1908.

`Pafrented Nov. 16, 1915.

2 SHEETS-SHEET 2.

'HANS GOLDSCHMIDT, 0F ESSEN-ON-THE-IRUHR, GERMANY; ASSIGNORTOGOLDSCHMIDT DETINNING' COMPANY, OF NEW YORK, N. Y., A CORPORATION 0F NEWJERSEY.

ELEGTROLYTIG POCESS OF DETINNING.

To all whom t may concern Be it known that I, HANS GoLDsoHMID'r, asubject of the King of Prussia, German Emperor, and resident ofEssen-on-the- Ruhr, Germany, have invented a certain new and usefulElectrolytic Process of Detinning, of which the following is a specification.

This invention relates to an electrolytic process of detinning, and themain object of the invention is to detin scrap by means of an alkalineelectrolyte in a more perfect manner than was done with prior processesof the same type.

In the electrolytic alkaline process of detinning, as practised prior tomy invention, it'wasy extremely diflicult to effecten even and thoroughdetinning, chiefly because of the difficulty experienced in .maintainingal proper circulation of the electrolyte through the single electrolyticcell in which it was customary to place the material to be detinned.This diiiiculty in maintaining the proper circulation of an electrolyteof substantially uniform quality, and at a sufiiciently high temperatureto produce the best results, made it impossible to circulate thealkaline liquid through a group of electrolytic cells mechanicallyconnected inseries,

or to keep the liquid in the proper condition for good and evendetinning. The difficulty of maintaining the propery circulation of anelectrolyte of propercondition and quality through a. plurality ofelectrolyti'c cells mechanically connected in a series is also due inlarge measure to the fact that the metallic connecting pipes throughwhich it would be necessary to circulate the liquid through the systemwould quickly become choked up as the result of electro-deposition oftin on the inner Walls of the pipes. this Velectro-deposition being'dueto a secondary and undesirable electrolytic action.' For these tworeasons chiefly it was extremely difficult to practise the alkalineelectrolytic process of detinning with any considerable degree ofsuccess prior to the discovery which I made that both of theseobjectionable features of the process of detinning' of this type couldbe eliminated by a proper organization of all the elements of theapparatus or system employed in carrying out the process. Thisorganization involved chiefly the provision of means for circulat ingthe electrolyte in such a manner that it would pass in a plurality ofpaths through Specification of Letters Patent. :I ifatelrted NGV, 16,1915, Application led February 5, 1908. Serial No. 414,439.

all the electrolyt'ic vessels of a series or sys- ,type of plantactually installed and used commercially, through a different one of thevessels of the system. By circulating the electrolyte in this manner afresh supply of the alkaline liquid was always delivered directly from asource of supply through suitable conducting pipes to each individualelectrolytic cell, the cathode vessel of each cell being thus connectedin the circulation system in parallel in a manner analogous to theconnection in parallel of various electrical devices in purely electricsystems. By circulating the electrolyte in this manner I found that itwas easy to circulate the electrolyte through a large number of cathode'and anode vessels of electrolytic cells and through the materialcontained in the anode vessels of said cells without danger of astoppage of the flow of the electrolyte through any cell of the system;and I also found that it was easy to maintain the alkaline electrolytein a perfectly Huid and uniform condition at a sufficiently hightemperature to do good detinning. Moreover, I devised means forpreventing the electro-deposition of tin on the inner walls of theconnecting pipes by secondary electrolytic action, and thereby1preventing the clogging or choking up of the pipes of the system andconsequent reduction of the areas of the openings through which theelectrolyte flowed. This I accomplish by specificI means which will hehereinafter de' scribed involving preferably the partial or nearlycomplete electrical insulation of inlet pipes from thel alkaline bath inthe different cathode vessels. This is a very important matter. as tinelectrolytically deposited from the bath in the electrolytic alkalineprocess of detinning is in a spongy state occupying considerable space,and if permitted to deposit on the walls of connecting pipes quicklychokes up the same.

I have found that b v thus organizing the whole system employed in' thealkaline electrolytic detinning process the choking up of the connectingpipes is prevented and the circulation of the electrolyte at a. uniformrate through openings unobstructed, except as they may be intentionallypartially obstlucted for the regulation of the flow, may

be readily maintained; ,while the alkaline liquid itself may be readilykept 1n the most perfect condition for detinning, that is, in aperfectly fluid state and at a uniformly high temperature, preferably ata temperature of from C. to 80o C., without difficulty. Vhen theelectrolyte 1s in this fluid Acondition and at this temperature it is ofsubstantially uniform composition and is in the best condition foretfecting thorough and even detinning of the niaterial in the anodevessels.

In order to accomplish the best results Il have found'that it isnecessary to supply electric current of very high amperage to thedifferent electrolytic cells. The current used in practice for detinningon a large scale is from 800 to 1000 amperes per square foot and currentof this density is circulated through each electrolytic cell of thesystem. An important feature of my ima proved process is therefore thecirculation of current of this high density through the system. Thiselectric current need not, however,v traverse the dierent electrolyticcells in parallel, but may pass through electrolytic cells connected inseries. In order to obtain the best results, however, it is desirable todivide the anode material of each cell up into small portions which maybe connected in parallel'so that the full amperage of the current maypass directly through each portion of the anode material.

Other features of my process which facilitate the circulation of theelectrolyte through the various electrolytic vessels and aid ineffecting even and thorough detinning of the materials contained in theanode vessels of the electrolytic cells, will be hereinafter describedin connection with the accompanying drawings, in which:

Figure 1 is a plan illustrating diagrammatically an electrolyticdetinning systemv embodying my invention; Fig. 2 is an end elevation` ofthe same; Fig. 3 is a detail of parts of two electrolytic vesselsillustrating the circuit connections thereof. Fig. 4 is a detailillustrating the supply reservoir and means for heating the` electrolytetherein. Fig. `5 'is a similar view of the return reservoir for theelectrolyte and means for heating the electrolyte therein. Fig. 6 is adetail illustrating one of the scrap-containing vessels or basketssupported in place in its cathode vessel.

Similar characters designate like parts in all the figures of thedrawings.I

Referring first to Fig. 1, which illustrates one way in which thevarious elements of a system constructed in accordance with my presentinvention may be combined, 1 designates a source of supply from which analkaline electrolyte may be delivered to the various electrolyticvesselsl of the system. This supply reservoir is preferably locatedabove the other elements of the system, 1n

order that the liquidmay flow therefrom while the other pipe 4 in asimilar manner supplies the electrolyte to another series of vessels.Two branch supply pipes, such as 5 and 6, lead in this case from themain supply pipe 3 to the electrolytic vessels or vats v of the firstseries, these vessels being designated by 7, 8,' 9 and 10 respectively.At their ends the branch supply pipes are shown as forked, the forksfrom the branch supply pipe 5 being designated by 11 and 12, and thosefrom the branch supply pipe 6 by 13 and 1,4. In a similar manner branchsupply pipes 15 and 16 leadfrom the main supply pipe 4, and each in turnis forked, these forks being designated by 17 and 18 for the branch pipel5, and by 19 and 20 for the branch pipe I16. The vessels `or vats ofthe second series ory roware designated respec` tively by 21, 22, 23 and24. The forked inlet pipes 11, 12, 13, 14, 17, 18, 19 and 2o arepreferably provided with suitable controlling means,such as valves, forgoverning the flow of the electrolyte into the vessels of the secondseries. These controlling means or valves for the first series ofvessels are designated by 25, and for the second series by 26. It willbe noticed thatthe pipes which supply the alkaline liquid to the dififerent electrolytic vessels decrease in cross section from the supplyreservoir 1 as they\ approach said vesesls. This is a matter of greatimportance in order to control the flow y of the liquid properly andprevent excessive flow while at the same time assuring a suffi` cientflow of the hquid at the` proper temperature and Iin the propercondition. I

'have found in practice that a good ratio for the respective inlet pipesis to provide a main pipe from the main reservoir of from three to fourinches in diameter, and to gradually decrease the areas of theintermediate pipes -until the forked pipes are reached, which may have adiameter of about three-fourths of an inch. Moreover,

itis desirable that the inlet ends of the forked inlet sections of thepiping be located above the level ofthe liquid of the respective baths,the inlet sections themselves being in the preferred construction madeof non-conducting material, such as hard rubber, these hard rubbersections, which are designated by 27, being slipped over the ends of theforked metallic pipes and preferably also being slightly above the levelof the bath. When the parts are constructed and combined in the systemin this manner stoppage of inlet pipes due to electro-deposition of tin,is avoided, and in addition the 'as 28 within said reservoir.

` proper How of the liquid, which is always under considerable pressurebecauseof the Ielevation of the supplyA reservoir, is assured. Thesupply reservoir will preferably be of large size for ,thei purpose of`keeping n the electrolyte at the proper temperature and in as uniform acondition as possible. In the construction shown the reservoir 1 (with areturn reservoir which will be hereinafter specifically described)should be capable of holding from one-third to one-half of the wholeamount of alkaline liquid contained in the system. In practice I haveused supply and return reservoirs the combined dimensions of which werefrom about ten to thirty cubic meters.

Inworder. to maintain the electrolyte in the supply reservoir 1 at theproper temperature and in the proper condition, the liquid is preferablyheated while in thereservoir, as for example, by means of a heater suchThis heater may be of the tubular variety, such as shown, and may besupplied with steam throughy suitable inlet and outlet pipes, such asv29 and 30. It will be noticed that in every instance the electrolyteenters each electrolytic vessel near one end thereof and at the upperside of the bath. In order that as complete a circulation of the liquidthrough the bath as possible may be obtained, it is preferable to placethe outlet from each vessel at the opposite end thereofv andsubstantially at the bottom of the vessel. This assures a thoroughcirculation of the alkaline electrolyte from the upper side of the bathat one end thereof to the bottom of the bath at the opposite end of thevessel, from which lpoint it may be permitted to ow out through suitableoutlet pipes which in practice may be arranged in a manner analogous tothat before described .with reference to the inlet pipes and arepreferably about two inches in diameter. Thus, two main outlet pipes,such as 31 and 32, run in this case parallel with and below the two rowsor series of electrolytic vesselsy 7 to 10 and 21 to 24. and areconnected to the bottoms of the different vessels, there being a.separate branch outlet from each vessel of the two series. This branchoutlet from each electrolytic vessel is of diHerent type from the branchconnections at the inlet side of the system. These branch outlet pipesare constructed as communicating vertical tubes 33 and 31, open at theirupper ends and connected at a point just below their'upper ends by ashort cross pipe 35. The pipe 33 connects with the lower end of theelectrolytic vessel, while the pipe 34 is connected directly to the mainoutlet pipe 31 or 32, as the case may be. Each one of the eightelectrolytic vessels in the two series has a connection therefrom to itsrespective main outlet pipe of the character just described. The objectof constructing the outlet from each electrolytic vessel in this manneris to prevent the level of the bath rising above a predetermined point,the parts of the system being so constructed and combined that theelectrolyte .will overflow from the open upper ends of the pipes 33 and34; whenever the conditions are such -that the electrolyte rises todhigh in the bath.

The lbranch outlet pipes just described lead the slightly cooledelectrolyte from -the main outlet pipes 31 and' 32 to a return lar tothat before described with reference i to the supply reservoir. Thesteam inlet and out-let pipes of the return reservoir are designatedrespectively by 38 and 39.

The connections between the various electrolytic vessels and the returnreservoir 36. may be either open or closed conduits or pipes; thesebeing interrupted at intervals by tanks, such as 40, to receive theslime resulting from ythe reaction.

From the return reservoir the circuit through which the electrolytetravels is completed by connections to the lhigh reservoir. Theseconnections preferably include a pump, such as 4l, forpumping'the'electrolyte up into the supply reservoir from the lowreturnreservoir. This pump is preferably placed at a sightly lower levelthan the low return reservoir in order that the electrolyte may flow bygravity into the pump. The pump can then readily force it up into thehigh supply reservoir, this being the more readily accomplished when theelectrolyte is brought into a more perfectly fluid condition by heatingin the low reservoir in the manner just described.

In order'to keep the electrolyte of the baths in as fluid a condition aspossible (and for the further purpose of electrically iso- 11i latingthe baths) it is desirable in practice to have each of the electrolyticvessels inclosed by a suitable non-conductor of heat and electricity.Both of these objects are acx complished by boxing the vessels, wooden12Hv boxes being preferably employed for the purpose, and an. insulatingairspace being left between the wooden box and the walls of the ironelectrolytic vessels. These boxes are designated respectively by 42.

The electrolytic vessels `7 to 10 and 21 to 24 of the system are usuallymade of castiron, and constitute the cathodcs of the ap-V paratus. Theanodes of the different electrolytic vessels may be of any suitableconthe tin from the scrap. The electrical conneotions ineach cell may beany suitable for the purpose. In this case I have illustrated a`plurality of parallelelectrical connections from a supplyconductor toeach anode of a cell. 'Ihe different cells of the two series are,however, in this construction connected in series with one another.

Fromal suitable source of energy 'such as the generator 44, current isfed to sectional supplyconduotors,i such as 45, there being one of themfor each electrolytic cell. Preferably these sectional conductors arenormally disconnected from one another, but are connected to the.cathodes of adjoining cells. lVhen a scrap-containing vessel 4or anodeisin place in a cell 'the circuit is comp leted from the sectionalconductor 45 at one side of the cathode vessel to the opposite sidethereof through the scrap and its container and the electrolyte, andcurrent can flow through the two elements of such cell. In eachinstance, however, th'e sectional supply conductor 45 is insulatednormally from the cathode, as is the basket 43.

It will be noticed that in the systemshown each gathode vessel containsa plurality. of anode baskets connected in parallel -in the circuit ofeach electrolytic cell. This permits the total quantity of tin scrapcon-v tained in any one cell of the systemy to be divided up into aplurality of smaller portions.

When it is necessary or desirable for any reason to cut out the electriccurrent from any cell of the "system, this may be accomplished by Ineansof a suitable switch, such for example as that shown 'at 46. This switchserves to connect vone end of a sectional supply conductor45 with anadjoining section of the supply conductor, thus short-circuiting thecell of that particular sectional supply conductor and directlyconnecting said sections of the supply' conductor through theintermediate switch. Each of these Sectional conductors 45 is preferablya copper rod or bar insulated from the wall of the cathode vessel. Astrip of wood, such as 47, is usually employed as the insulating supportfor this conductor, said strip being fastened on the edge of the.vessel. ductor thoughinsulated from its own cath- 65 Each sectionalconode vessel is of course electrically connected with-the other cathodevessel. I prefer to usev an angular bond, such as 48, which is solderedor welded to the cathode and has its upper edge in line with that of thesectional 7ov conductor of the cathode vessel to which it is fastened.Whenever two adjoining sectionall supply conductors are connected bytheir switch 46, the baskets in the short-circuited cell may be readilyremoved. Moreover, the

controlling valve in the inlet pipe for that cell may be closed, theelectrolyte drawn olf from the cathode lvessel, and that vessel itselfput out of action without interrupting the detinning process inthe othercells of l the series.

Normally the electric current Hows without interruption through all thecells of the fsystem. The current used, order to vaccomplish the bestresults, that is, the most 85 economical detinning, will preferably beone of very high amperage, say from 800 to 1,000 amperes per square footor more. The

use of current of this high density is a matter of much importance andwas only deter- ,mined upon after exhaustive experiments which showedthat it was the most desirable under all conditions present in a largecommercial detinning plant.

The compositlon of the electrolyte for practical detinning on acommercial scale is also a matter of very great importance. I. prefer touse a mixture of stannate of soda and caustic soda with an excess of thecaustic soda. The alkaline electrolyte contains also carbonate'of soda,as the alkali takes up and unites with carbonio acid in the air. With anelectrolyte of tliis composition the proc-A ess carried on is acontinuous one because of the regeneration of the liquid asit circu-,lates through. the system.

,What I claim is: An improvement in the art of detinning, which consistsin immersing ay plurality of lots of scrap tin in each of a plurality of1104 alkaline baths contained in metal receptacles, supplyingelectrolyte at a high -tem- `perature to and withdrawing it from themetal receptacles separately and passing an electric current of highamperage through each of said receptacles, its `bath and the tin scrap,said current being distributed at each receptacle in parallel throughthe several lots of tin scrap.

Signed at New York, in the county of New York, and State of New York,December, lA. D. 1907.

' I-IANS GOLDSCHMIDT.

Witnesses:

GHAS. F. DANE, HUBERT E. Rooms.

